linux-kernel - Re: [patch] SLQB slab allocator (try 2)

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Date:	Tue, 17 Feb 2009 19:11:57 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, Mel Gorman <mel@....ul.ie>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Nick Piggin <npiggin@...e.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lin Ming <ming.m.lin@...el.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Subject: Re: [patch] SLQB slab allocator (try 2)

On Tue, Feb 17, 2009 at 12:05:07PM -0500, Christoph Lameter wrote:
> Well yes you missed two locations (kmalloc_caches array has to be
> redimensioned) and I also was writing the same patch...
> 
> Here is mine:
> 
> Subject: SLUB: Do not pass 8k objects through to the page allocator
> 
> Increase the maximum object size in SLUB so that 8k objects are not
> passed through to the page allocator anymore. The network stack uses 8k
> objects for performance critical operations.
> 
> Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
> 
> Index: linux-2.6/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slub_def.h	2009-02-17 10:45:51.000000000 -0600
> +++ linux-2.6/include/linux/slub_def.h	2009-02-17 11:06:53.000000000 -0600
> @@ -121,10 +121,21 @@
>  #define KMALLOC_SHIFT_LOW ilog2(KMALLOC_MIN_SIZE)
> 
>  /*
> + * Maximum kmalloc object size handled by SLUB. Larger object allocations
> + * are passed through to the page allocator. The page allocator "fastpath"
> + * is relatively slow so we need this value sufficiently high so that
> + * performance critical objects are allocated through the SLUB fastpath.
> + *
> + * This should be dropped to PAGE_SIZE / 2 once the page allocator
> + * "fastpath" becomes competitive with the slab allocator fastpaths.
> + */
> +#define SLUB_MAX_SIZE (2 * PAGE_SIZE)

This relies on PAGE_SIZE being 4k.  If you want 8k, why don't you say
so?  Pekka did this explicitely.

	Hannes
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